The Importance of Vapor Testing

In this interview, Dr Damiano Cattaneo talks about the importance of dynamic vapor sorption and how it is a vital measurement in various industries such as pharmaceuticals and biomaterials.

Could you give me a brief overview of Dynamic Vapor Sorption technique and its importance?

Dynamic Vapor Sorption, or DVS, is a gravimetric technique that records the mass of the sample as it varies with changes in temperature and/or humidity (or P/P0). Here P is the vapour pressure and P0 is the saturation vapour pressure. P/P0 is equivalent to % relative humidity for water. Typically, the humidity of the environment is changed in a stepwise fashion, whilst the temperature is held constant. Throughout the experiment the mass of the sample is recorded, this will show the kinetics of the sample’s interaction with the vapours. The data can also be plotted as isotherms (where mass uptake vs P/Po at a constant temperature is displayed) and this allows the study of the sample’s response to the changes in P/Po. The experiment can be carried out using water or organic solvents as well as both at the same time to generate different partial pressures. As indicated by the name, the experiments are all carried out in dynamic mode; where the partial pressure or humidity is not statically dosed but rather constantly flowed over the sample with the aid of a carrier gas (nitrogen or air). Dynamic experiments allow the sample to reach equilibrium at a faster rate than static experiments.

Schematic representation of the DVS Endeavour hardware.

In the DVS Endeavour we are able to run up to 5 experiments simultaneously allowing for the collection of high-quality data in a fifth of the time.

DVS Endeavour sorption and desorption isotherm data collected on a reference material used to test repeatability.

How is the DVS technique crucial in the analysis of the physical and chemical properties of different materials?

The DVS instrument can simply be described as a tool that allows the user to answer specific questions and collect information regarding the properties of new or even well-known materials. The accuracy and the versatility of our gravimetric technique can aid in the understanding of particular sample behaviours under specific temperature and partial pressure conditions. Even from the analysis of a simple isotherm sorption experiment it is possible to calculate in-depth data such as the BET surface area and micro and mesoporous porosity calculations. Each experiment can also be customized and tailored towards specific samples, for the calculation of such parameters as diffusion and permeability coefficients as well as an estimate of the heat of sorption. The DVS can be used to carry out a complete study of sample affinities towards a series of solvents as a single or a multi-component sorption (competitive sorption) experiment, therefore monitoring the chemical and physical properties of the samples in question.

What is the advantage of measuring sorption using different solvents on the same sample?

The DVS technique was originally designed to only perform water sorption. However, a lot more information can be obtained from the use of organic solvents as probes. Organic solvents are often necessary in the development, characterisation and crystallisation of the samples; therefore, it is important that we investigate how these solvents interact with the material itself. The shape and type of isotherm observed experimentally depends upon the interaction between the probe and the sample. Some probes might only adsorb on the surface of the material (which can be used for BET calculations for example) while other probes can absorb through the bulk of the material resulting in structural change (which can be reversible or irreversible). The DVS Endeavour will allow you to investigate and distinguish between the two.

DVS Endeavour sorption and desorption isotherm data collected on a single sample using multiple different solvents.

What are the benefits of using two solvents at the same time in a DVS experiment and how is this achieved?

Any DVS study will always begin with data collection using one solvent at a time. The data collected from these initial experiments can give us important information in regards to the properties of the material. However, the data obtained usually represent the performance of the material under ideal conditions. In reality, whenever a material is exposed to a specific process it is usually in the presence of multiple solvents at the same time, as opposed to a single solvent. The sorption capacity of the sample can really be affected by the presence of a mixture of solvents rather than a singular probe. For example, many zeolites and metal organic frameworks (MOFs) have extremely high sorption capacities when exposed to an organic solvent after an activation step (eg. Preheating at 150C) under ideal conditions (eg. Nitrogen flow). The presence of even 5-10% background relative humidity (which represents a more realistic environment) can potentially reduce the total sorption capacity by an order of magnitude.Our DVS technique will allow you to perform accurate evaluations of materials under different conditions in the presence of multiple solvents at once. The partial pressure of the two solvents can be controlled in multiple ways. For example, the ratio of the two solvents can be maintained throughout the experiment during absorption or desorption or the generation of one solvent is held constant while the other one is increased or decreased as the experiment proceeds.

DVS Endeavour sorption and desorption isotherm data collected using one single solvent (butanol and hexane) and a mixture between the 2 solvents (mixture of 50% butanol and 50% hexane).

How does the DVS Endeavour help your users to get their solutions?

The DVS Endeavour is an instrument that monitors the change in mass of five samples simultaneously as a function of time at given partial pressures of solvent. The Endeavour is specifically designed to provide the advantage of a high throughput instrument with the accuracy and versatility of a single balance such as with the DVS Resolution.

Thanks to the multi-balance design, the most obvious application of the DVS instrument is batch-to-batch variability and formulation studies. The greatest advantage of using the Endeavour is the fact that five experiments can be conducted at once, saving time and money. Moreover, the DVS Endeavour can be equipped with a speed-of-sound sensor (SOS sensor) as well as accessories such as a camera and preheaters which makes it just as versatile and accurate as the DVS Resolution. The SOS sensor is a sophisticated detector that uses time-of-flight measurements to calculate the concentration of a solvent dispersed in a carrier gas at a constant temperature.

Schematic representation of the SOS sensor.

By measuring the difference of time-of-flight between the pure carrier gas and the carrier gas/solvent mixture the sensor is able to accurately calculate the partial pressure generated at each stage of the experiment. The SOS sensor can also be used to control the concentration of solvent delivered to the sample. This technology is patent pending and will change how organic and moisture sorption isotherms are measured and controlled in the future.

With its SOS sensor, the multiple accessories and the mutli-balance capacity, the DVS Endeavour remains the most robust instrument offered by SMS to date. The Endeavour will enable the users to successfully characterise any type of material, whether its pharmaceutical, a porous material, a polymer, food or building materials to name but a few.

How does SMS stand out from other companies in your field?

Surface Measurement Systems delivers scientific solutions not just instruments. SMS develops and engineers’ innovative experimental techniques and instrumentation for physico-chemical characterisation of complex solids. What I think sets us apart from other companies is the relationship we develop with all our users and our determination to help each user find the right solution. Our high level of expertise and our research-oriented mindset allows us to readily adapt to customer requests from the point of view of software, hardware and data analysis. We not only offer the best possible instruments available on the market but we also offer continued advanced training and customer support for problem solving, method creation, data analysis and hardware and software development.

SMS offers a wide range of characterisation instruments which have helped to solve a number of difficult problems in the pharmaceuticals, biomaterials, polymers, catalysts, chemical, cosmetics and food industries. Our instruments are also used by hundreds of leading laboratories and universities worldwide.

What are the plans for moving forward with product development for SMS?

We are a research and development driven company. We are constantly looking into the development of new accessories or improvements for existing products as well as the design and implementation of completely new instruments. In the last two years SMS has successfully launched three new products (DVS Adventure, Resolution and Endeavour), a entirely new type of sensor and has adapted accessories such as camera, preheater, NIR and Raman to all these products. This proves that we are constantly looking to the next step, be it a simple improvement of existing hardware or software or be it the next slice of science in a box.

Where can our readers find out more about DVS, and the DVS systems provided by    Surface Measurement Systems?

AZo readers can find more information about DVS products on the Surface Measurement Systems website, conferences or scientific posters presented at local or international meetings. DVS data is also published in peer reviewed scientific journals.

About Dr Damiano Cattaneo

Dr Damiano Cattaneo is an Instrument Scientist of Surface Measurement Systems and senior specialist for the DVS product. Damiano obtained his PhD in Chemistry (Material Science) at the University of St Andrews (UK) in December 2015. His research project was focused on using porous materials for biomedical applications. Specifically, he investigated the development of porous coordination polymers (MOFs, COFs and Porous Organic Cages) and Zeolites as gas and drug delivery systems for biomedical devices. Dr Cattaneo has a Masters degree in Medicinal Chemistry (Pharmaceutical Chemistry and Technologies) from Università degli Studi di Milano (IT). During the last year of his Masters degree he also worked as a researcher on drug discovery and total synthesis of anti-Parkinson drugs (inhibitor of muscarinic receptors) at the Department of Pharmaceutical Sciences “Pietro Pratesi” (Milan, Italy).

Since joining SMS in 2016, he has worked on the development of advanced in-situ experimental surface science techniques using molecules as probes for studying catalysts, zeolites, MOFs, polymers, pharmaceuticals, composites and cement materials under relevant industrial conditions. Dr Cattaneo has also helped with the development, testing and launch of the new DVS Adventure, Resolution and Endeavour products.